Treasury Stock (Details) (USD $)	6 Months Ended				1 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Repurchase Programs	Jun. 30, 2012 Repurchase Programs	Jan. 31, 2012 Repurchase Program 2012	Jun. 30, 2013 Repurchase Program 2012	Jun. 30, 2013 Employee benefit plans repurchases	Jun. 30, 2012 Employee benefit plans repurchases
Shares repurchased in connection with:
Common stock authorized for repurchase					$ 300,000,000
Amount remaining for purchase under the repurchase program						2,000,000
Total	$ 27,118,000	$ 302,099,000	$ 18,122,000	$ 294,787,000			$ 8,996,000	$ 7,312,000
Total (in shares)	368,600	6,391,100	237,900	6,238,700			130,700	152,400